Forecasting the Cross-Correlation of the CSST galaxy survey with the FAST HI Intensity Map

TL;DR

This study demonstrates that cross-correlating optical galaxy data from CSST with HI intensity maps from FAST can significantly improve the measurement precision of HI abundance at redshift around 0.3.

Contribution

It introduces a method to enhance HI signal detection by cross-correlating CSST galaxy data with FAST HI intensity maps, validated with simulated data.

Findings

High correlation between HI and optical galaxies across samples.

Potential to measure HI abundance with 0.6% error at z~0.3.

Effective in improving signal-to-noise ratio for HI measurements.

Abstract

The cross-correlation of optical galaxies with the neutral hydrogen (HI) radiation intensity can enhance the signal-to-noise ratio (SNR) of the HI intensity measurement. In this paper, we investigate the cross-correlation of the galaxy samples obtained by the spectroscopic survey of the China Space Station Telescope (CSST) with the HI Intensity mapping (IM) survey of the Five-hundred-meter Aperture Spherical Telescope (FAST). Using the IllusitrisTNG simulation result at redshift $0.2 \sim 0.3$, we generate mock data of the CSST survey and a FAST L-band drift scan survey. The CSST spectroscopic survey can yield a sample of galaxies with a high comoving number density of $10^{-2} (\unit{Mpc}/h)^{-3}$ at $z \sim 0.3$. We cross-correlate the foreground-removed radio intensity with the CSST galaxies, including both the whole sample, and red and blue galaxy sub-samples separately. We find that in all cases the HI and optical galaxies are well correlated. The total HI abundance can be measured with a high precision from this correlation. A relative error of $\sim 0.6\%$ for $\Omega_{\rm HI}$ could be achieved at $z\sim 0.3$ for an overlapping survey area of $10000 \unit{deg}^2$.